1. Field of the Invention
The present invention relates to a receiver which receives a broadcast radio wave, performs a variety of modulation processing on an audio signal included in the broadcast radio wave, and retransmits the audio signal on a radio wave different from the received radio wave.
2. Description of the Related Art
In recent years, new forms of information media have increased, such as the satellite broadcasting, digital broadcasting and the like. It is quite useless to purchase tuners dedicated to these new media and further provide audio equipment such as an amplifier, speakers, and the like for each tuner because the devices become duplicated. This also creates space problems for installing new devices, and cables which should be routed and connected between components. Particularly, the problem is severe for vehicle-equipped devices because a vehicle has only a limited space available for equipment.
To cope with this problem, some conventionally known receivers for television broadcasting and satellite broadcasting, have a function of extracting only an audio signal from received and reproduced information signals, frequency modulating (FM) the audio signal, and retransmitting the frequency modulated audio signal as a weak radio wave (see Laid-open Japanese Patent Applications Nos. 6-268936, 11-331000). These receivers having a retransmission function generally set the frequency of a FM radio wave to be retransmitted within the frequency band of the FM broadcasting (76-90 MHz in Japan). Therefore, a receiver having such a function permits the user to hear only an audio signal extracted from the television broadcasting and satellite broadcasting, using an ordinary FM radio.
However, when these receivers having the retransmission function experience a deteriorated receiving state of an originally received radio wave, the quality of an audio signal extracted from the received radio wave is also degraded. As a result, the S/N ratio becomes lower in the audio signal included in a retransmitted FM radio wave.
Therefore, with a television receiver for analog broadcasting having such a function, a deteriorated receiving situation results in a gradual increase in noise in an audio signal included in a retransmitted FM radio wave. On the other hand, with a receiver for digital broadcasting, which performs an error correction during a receiving and reproducing operation, noise will not increase even if the receiving situation deteriorates to some degree. However, when the deteriorated receiving situation exceeds a limit of the error correction, the reception quality suddenly degrades. This results in a sudden increase in noise in an audio signal included in a retransmitted FM radio wave.